A similar setup that a buggy uses should work. 7-8xl on 4s with a MM. Maybe a 9xl on 5s with a quark 125. Neu 1512(1800-200kv) with a quark125(MM?) on 4-5s. Go HV and buy this and run it on 8s with low gearing, like a 10 tooth pinion!
http://www2.towerhobbies.com/cgi-bin...?&I=LXGCX1&P=7
That might be a bit much, but you could use 2500mah lipos on an 8s setup! Easier to package and possibly lighter?!